Polymer composites used in devices such as engines, ducts, machinery, and aircraft parts are often required to be electrically conductive, lightweight, structurally strong and stiff, so as to confer anti-static and electromagnetic shielding properties. In particular, polyimides (PIs) are an important class of structural polymers used in the microelectronics and aerospace industries, because of their outstanding thermal stability and mechanical properties. Carbon nanotubes (CNTs) have been considered to be a good additive for making high-performance conductive polymer composites because of their excellent electrical conductivity values in the range of about 103 to 106 S cm−1, ultra-high strength, large aspect ratio, and low density. However, the electrical conductivities achieved in polyimide/CNT composites have typically been low, in the range of about 10−1 S cm−1 for a nanotube/polyimide composite with 5 wt % nanotubes. Attempts to improve electrical conductivities of polyimide/CNT composites have been hampered by low CNT content (about 10 wt %) and poor dispersion of the CNTs.
Various research groups have carried out work to increase the electrical conductivity of CNT/polymer composites. Even though electrical conductivities in the range of 17 S cm−1 to 200 S cm−1 have been obtained in composites with a CNT content of more than 75 wt %, these materials employ special nanotubes and/or unconventional composite processing techniques, such as vacuum filtration or coagulation spinning, to result in high nanotube content and alignment, which leads to high processing costs and complicated processes which are not suitable for mass production.
Other composite processing techniques, such as casting and resin transfer molding, are not able to achieve the high carbon nanotubes loading. This in turn leads to low electrical conductivity of CNT/polymer composites formed using such methods, with most composites having conductivity values in the range of less than 1 S cm−1.
In view of the above, there remains a need for an improved method for forming a polyimide-carbon nanotube composite that addresses at least one or some of the above-mentioned problems.